Where does your timber come from? Genetic analysis may soon tell you

Illegal trade in tropical timber costs countries billions of dollars in revenue each year and threatens regional and national biodiversity.

Researchers tested the potential of two genetic analysis techniques to pinpoint the geographic origin of timber trees and thus verify claims that trees are harvested in legal quantities from permitted locations.

They successfully assigned samples of tali, a highly exploited African timber tree, to the forest concession of origin using genetic markers.

Their findings suggest that genetic analysis can differentiate the geographic origin of tropical timber at the scale of forest concessions and can serve as forensic tools to enforce timber trade legislation.

Researchers have identified a genetic analysis technique that pinpoints the harvest location of trees—a breakthrough that could help officials detect illegally traded timber.

The multi-national research team tested the potential of two kinds of genetic analysis to differentiate the geographic origin of timber samples at the scale of individual forest concessions.

Their tests on hundreds of samples suggest that the genetic signature of wood differs by source location and can be used to match a given piece of timber to its source location at a relatively fine scale.

Previous studies estimates that 30 to 90 percent of the volume of tropical timber traded by export countries is illegally harvested. The illegal trade includes trees from protected species, as well as from permitted species taken from protected areas and other no-take zones.

Illegal trade costs exporting countries billions of dollars in tax and private sector revenue, as well as their unique biodiversity, so officials have turned to species identification techniques, such as chemical analysis and wood structure analysis. These methods have advanced the ability to locate the origin of timber samples on regional scales but have not been sufficient to determine whether the trees were harvested from within legal forest concessions. Forged forest management plans, fake export permits, and mixing timber of different origins allow criminals to “launder” timber illegally sourced from prohibited locations.

Blind testing

Seeking a way to identify the source locations of timber trees independent of documentation, the researchers explored whether two key characteristics of wood samples—microsatellite genetics and stable isotopes—could be used to differentiate among trees taken from different forest concessions, and at what spatial resolution.

The researchers collected 394 wood samples from 134 tali (Erythrophleum spp.) trees, a group of highly traded African timber species. The team worked in five logging concessions, between 14 and 836 kilometers (9 to 519 miles) apart, in Cameroon and the Republic of Congo.

As trees take in water and nutrients from soil, they absorb certain isotopes of chemical elements, such as hydrogen, carbon, nitrogen, and oxygen. The amounts of each isotope vary from place to place, so measuring the relative abundance of stable isotopes in plant tissues can identify the tree’s geographic origin.

A first step in measuring stable isotopes is the extraction of cellulose from wood samples, shown here. Photo credit: Mart Vlam

“The isotopic composition of a tree reflects local processes at the growing place of the tree, like rainfall and soil composition,” co-author Pieter Zuidema of the Forest Ecology and Forest Management Research Group at Wageningen University in the Netherlands told Mongabay-Wildtech in an email. “These processes are ‘imprinted’ in the wood. With this chemical ‘fingerprint’ we should also be able to trace back the origin of the timber. In the case of the Tali study, this didn’t work, probably because distances between sites were insufficient.”

DNA microsatellites, meanwhile, are commonly used in forensic analyses, Zuidema said. Microsatellites are pieces of DNA that repeat and can mutate faster than other DNA, leading to patterns that vary without affecting the plant’s functioning. This variability makes it possible to distinguish groups of trees within a single species, so it can be used to measure the relatedness between species or individuals.

“Trees that are more closely related (in terms of parentage) usually are located at smaller distances from each other than trees that are less related genetically, Zuidema said. “So, there is a positive relation between the genetic ‘distance’ between trees (which we can measure) and the geographic distance between trees (which we would like to infer or check). This relation allows [us] to trace the origin of trees.”

The researchers developed a reference database for the genetic microsatellite markers using samples from across the study area and ran “blind” tests on remaining samples.

‘A great score’

“I had 12 pieces of timber of which I knew the origin but the genetic specialists at Wageningen Environmental Research didn’t,” lead author Mart Vlam, also of the Forest Ecology and Forest Management Research Group, said in a statement. “I gave them the samples and asked them to identify which concessions they came from. They got it right 92% of the time—that’s a great score.”

The team found that the microsatellite analyses correctly assigned timber samples to the concession of origin, even those less than 20 kilometers (12 miles) apart. In contrast, at this scale, the combined analysis of carbon, nitrogen and oxygen stable isotopes did not categorize the samples correctly.

“Isotopic differentiation may be possible at larger spatial scales or with stronger climatic or topographic variation,” the authors say in their paper.

“The fact that we can accurately differentiate the origin of timber down to a 14 km radius is new,” Vlam said. “Previous studies only managed to do that on a much larger spatial scale.”

What’s next?

The capacity of genetic analyses to differentiate the geographic origin of a key tropical timber species at the scale of forest concessions demonstrates their potential as forensic tools to enforce timber trade legislation, say the authors in their paper.

“A blind test as we did in this article closely resembles real-world sample testing,” co-author Pieter Zuidema said in an email. “The ‘only’ thing we need are adequate reference set[s] against which the blind tests can be performed.”

Moreover, the ability to identify timber harvested illegally from protected areas and other no-take zones as close as 14 kilometers from a legal logging concession could translate into a tool to help managers and other officials fight the illegal timber trade.

If applicable to other species and regions, the technique could enable trade officials to verify tree harvest documentation.

“But a lot needs to be done before these tests can be used as evidence in court,” Zuidema said in a statement. “We need to collect timber samples from a much larger area and our analyses and labs will have to meet strict criteria. We can’t do that on our own, so we are collaborating in a worldwide network of researchers, labs and authorities.”